From: Jorge Ramirez-Ortiz <jramirez@baylibre.com>
To: Mark Brown <broonie@kernel.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [RFC] regmap: allow volatile register writes with cached only read maps
Date: Wed, 9 May 2018 13:49:21 +0200 [thread overview]
Message-ID: <65607fde-d0e9-0f08-3042-f6a58b760896@baylibre.com> (raw)
In-Reply-To: <20180509083919.GU13402@sirena.org.uk>
On 05/09/2018 10:39 AM, Mark Brown wrote:
> On Wed, May 09, 2018 at 12:06:09AM +0200, Jorge Ramirez-Ortiz wrote:
>> Regmap only allows volatile access to registers when the client
>> supports both reads and writes.
>>
>> This commit bypasses that limitation and enables volatile writes to
>> selected registers while maintaining cached accesses on all reads. For
>> this, the client does not need to configure the reg_read callback.
> I don't understand what voltile access means for write only devices.
> Volatile means that we don't read the cache but go direct to the
> hardware so if we can't read the hardware that's pretty redundant, a
> volatile read that goes to the cache is just a default read.
oops, sorry will try to be a bit more clear with an example.
This patch tries to support a map that provides:
1. only cached reads: (as a consequence every regmap write must succeed).
2. cached writes: do not access the hardware unless the value differs
from what is in the cache already or (3) applies.
3. support for selectable volatile writes: those that will always access
the device no matter what the cache holds.
Something like this:
static const struct regmap_config foo_regmap = {
.reg_write = foo_write_reg,
.reg_bits = 32,
.val_bits = 32,
.reg_stride = 1,
.volatile_reg = foo_volatile_reg,
.max_register = CODEC_ENABLE_DEBUG_CTRL_REG,
.reg_defaults = foo_reg_defaults,
.num_reg_defaults = ARRAY_SIZE(foo_reg_defaults),
.cache_type = REGCACHE_RBTREE,
};
I dont think - I could be wrong- that this is something that we can
support today since the current code seems to require that the regmap is
readable (ie, that it implements reg_read).
But it could also be that I am missing something in my config? This is
why I sent an RFC instead of a PATCH, because I am not 100% sure that I
am not missing something.
next prev parent reply other threads:[~2018-05-09 11:49 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-08 22:06 [RFC] regmap: allow volatile register writes with cached only read maps Jorge Ramirez-Ortiz
2018-05-09 8:39 ` Mark Brown
2018-05-09 11:49 ` Jorge Ramirez-Ortiz [this message]
2018-05-11 2:00 ` Mark Brown
2018-05-11 10:29 ` Jorge Ramirez-Ortiz
2018-05-13 2:22 ` Mark Brown
2018-05-17 7:12 ` Jorge Ramirez-Ortiz
2018-05-17 17:04 ` Mark Brown
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